Abstract
On 12 May 2008 at 06:28 UT a major earthquake of magnitude 8.0 struck Wenchuan County (31.0° N, 103.4° E) in southwest China. Ionospheric total electron content (TEC) values, derived from a network of 58 global positioning system (GPS) receivers over China and nearby countries, were used to investigate the ionospheric precursor of the great earthquake. The observations revealed that there was an anomalous enhancement in TEC (100% increase on the 15-day median) during the afternoon–evening sector on 9 May 2008 while geomagnetic conditions were quiet (Kp ≤ 2). The TEC variations on the west side and east side of the epicentre show large dissimilarity on 9 May 2008. By constructing the longitude/latitude TEC map, the distribution of the region predominated by increased TEC values was shown to be localized at longitudes 90–130° E. Our results suggest that this abnormal enhancement was most possibly a seismo-ionospheric signature.
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